Japanese firm Mitsui & Co is planning to invest 9.6bn yen ($124m) in the Kestrel mine extension in Queensland, Australia, due to a recent increase in development costs.
Mitsui holds a 20% stake in Kestrel Joint Venture, which owns the project, and the remaining 80% stake is held by Rio Tinto.
The Kestrel mine extension will require a total of 48bn yen ($621m) in additional capital expenditure.
Currently, the Kestrel mine produces about 4Mtpa of metallurgical and thermal coal.
The extension is expected to increase the operation period of Kestrel by 20 years, with estimated coal production of 6.5Mtpa.
The total capital expenditure of the project, including the additional capital expenditure, will be about 157.6bn yen ($2bn), while Mitsui's total capital expenditure will be 31.5bn yen ($407m).